1. Field of the Invention
The present invention relates to a roller electrode for use in a continuous electroplating process in which an article is passed along a horizontal pathway, more particularly to a roller electrode which is capable of providing a stable voltage to the article.
2. Description of the Related Art
Electroplating is used in a manufacturing process for electro-depositing a layer of metal, such as nickel, cadmium, copper, silver, zinc or gold, on a surface of a product for the purpose of protection or decoration or for producing a printed circuit board.
FIG. 1 illustrates schematically a conventional electroplating process which generally involves immersion of an article 11 to be plated and a pure metal 12 in a suitable electrolyte solution 14 that is received in an electroplating tank 13. The metal 12 is formed as an anode 15, while the article 11 is formed as a cathode 16. When a direct current is applied, the metal ions contained in the electrolyte solution 14 move toward the article 11 and are reduced and deposited on the article 11. The pure metal 12 is dissolved to form the metal ions which are supplied to the electrolyte solution 14. In conducting the aforementioned dip-type electroplating process, the article 11, such as a printed circuit board substrate, must be hung above the electroplating tank 13 and then lowered for dipping into the electrolyte solution. In addition, frequent addition or replacement of the pure metal 12 is required for maintaining a sufficient ion concentration in the electrolyte solution 14. Therefore, the dip-type electroplating process is relatively complicated, labor consuming and costly.
In recent years, a continuous electroplating process has been developed to overcome the disadvantages of the dip-type electroplating process. Referring to FIG. 2, an article 21, such as a printed circuit board substrate, is passed smoothly through a plating tank 23 which contains an electrolyte solution 24 by means of a pair of negatively-charged roller electrodes 20 and a plurality of pairs of advancing rollers 25 which are in rolling contact with the article 21. An opposite pair of anode boards 22 are provided in the electrolyte solution 24 on two opposite sides of the article 21. The negatively-charged roller electrode 20 are in rolling contact with the article 21 for forming the article 21 into a cathode.
In the continuous electroplating process, the stability of the voltage provided by the roller electrodes 20 affects dramatically the quality of the coating plated on the article 21. It is thus desired to provide a roller electrode which is capable of providing a stable voltage to an article during rotation of the roller electrode.